Diamond is the hardest known material, widely used in industry both in tools for cutting, drilling and other operations, and in parts subject to wear. However, diamond use and performance in these applications can be restricted by several properties of diamonds. Firstly, diamonds are difficult to attach to tools or wear parts, due to the chemical inertness of diamond and also its poor wettability by molten metals. Secondly, diamonds can be oxidised or graphitized at the elevated temperatures often encountered during the manufacture or operation of such tools or wear parts. Graphitization is the transformation of hard diamond into soft graphite, and occurs at elevated temperatures when diamond is in contact with nickel, cobalt, iron and other metals that are catalysts of the diamond graphitization process. These metal catalysts are often used during the manufacture of synthetic diamonds and when sintering polycrystalline diamonds, and also are present in the cemented carbide parts often used to support diamonds, for example in oil drill bits incorporating polycrystalline diamond cutters. When diamonds are in contact with these metals, they become susceptible to graphitization, and this limits the maximum temperatures at which these can be used to below 400 to 500° C. This not only limits the use of the diamond tools, but it also restricts the use of high temperature manufacturing processes such as casting, brazing, and thermal spraying often employed in the production of oil drilling tools, stone cutting saws and other diamond tools and wear parts. Molten iron-group metals can quickly dissolve diamond even through a limited contact area.
Previous attempts to use coatings to improve the retention of diamonds and at the same time to protect diamonds from oxidation and graphitization have not produced satisfactory results.